1. Field of Invention
The invention relates to a multilayer structure, which is particularly suitable for the anti-scratch sealing and decorative metal finishing of topographically defined polymer surfaces, as well as to the vacuum-technical methods for building up the layer series.
2. Related Art
As a result of the constantly increasing requirements with respect to aesthetic (luster, color) as well as functional (scratch-resistance, impact-resistance) appearance of surfaces on molded parts, particularly also in the area of molded plastic parts, attempts have long been made to improve the known and in part deficient coatings for plastic materials. As indicated in the above, these coatings have to meet several functions, must simultaneously adhere well to the molded part provided with the coating, and must be extremely resistant.
The coating methods and coatings known from prior art, for example, comprise wet-chemical processes such as the electroplating, but also vacuum methods such as the PVD (physical vapor deposition) technique. Methods of this type are also used for coating molded parts.
Reference DE 195 23 442 A1 thus discloses methods for coating articles made of metals or metal alloys, wherein one coating is deposited with the aid of the CVD (chemical vapor deposition) technique. In the process, a quartz-type coating is deposited on the molded part to generate a protective layer by converting a reactive gas mixture, comprising oxygen and an organic silicon-containing compound, with the aid of an electric gas discharge reaction to a quartz-type coating.
Reference DE 199 01 834 A1 discloses a multi-stage coating method for depositing various layers onto plastic substrates. In the process, layers such as sub-layers, barrier layers, anti-scratch layers, and sliding layers are generated through a conversion of oxygen with silicon-organic compounds. The methods described for this process are vacuum methods, involving the generating of plasma.
The disadvantages of the known methods and the advantages of the method and/or the coating according to the invention are briefly summarized in the following.
1. Coating Method Involving Electroplating
Owing to the very different processing techniques (vacuum coating technique as compared to the wet-electrolytic coating technique), the differences between the method described within the framework of this application and the electroplating method are serious and, as a rule, prove to be advantageous. Examples to be mentioned here are the noticeably reduced danger to the environment, the higher flexibility of the deposited metals, and the less problematic masking and structuring.
2. Vacuum Coating Methods
With the aid of modern vacuum-coating methods (for example PVD and CVD techniques), a plurality of layers and layer systems can be generated, which can raise the quality of the surface finish of the coated body. The use can result from an interest in reducing wear and friction, or the desire for raising the decorative appearance of the surfaces, or a combination of both. However, since the invention according to this application is not limited to silicon-containing layers, the present invention permits a broader range of material combinations and layer combinations.
A review of the relevant professional literature shows that hard, wear-resistant layers and/or layer systems (these are hard material coatings, for the most part involving nitrides, carbides, carbo-nitrides, oxides of metals or metal alloys) are primarily used in the field of tool technology and machine technology—meaning they are used on metal substrates.
With respect to this, see: Klaus W. Mertz, Hermann A. Jehn, “PRAXISHANDBUCH MODERNE BESCHICHTUNGEN” (Operating Manual for Modern Coatings), Carl Hanser 2001, Chapters 1.2, 1.3, Tribological Layers.
We also point to the same source with respect to using vacuum-coating methods for plastic parts, primarily with respect to generating layers with optical, decorative and electrical functions. Prior art already discloses process patents for forming SiOx compounds, used for generating anti-scratch sealing coats on transparent polymer materials.
Combining hard material layers in a composite structure with polymer materials so far is viewed as basically very problematic because of the expected contrast in the profile of characteristics (hardness, plasticity, thermal coefficient of expansion).
The text by Markus Riester, “BERICHTE AUS DER CHEMIE, TITANNITRID AUF THERMOPLASTEN” (Reports from the Field of Chemistry, Titanium Nitride On Thermoplastic Materials), Publishing House Shaker, 1998, page 17, overview of samples, page 64, crack formation, teaches that when hard material layers are deposited (here: TiN or Ti/TiN—multilayer systems (2 to 6 double layers)) on extremely smooth polymer surfaces, the layer structure has a high tendency to form cracks during the build-up of the layers, starting with a layer thickness level of 0.06 μm.
Problem Definition
The problem definition follows from the aforementioned prior art and involves providing a layer structure which allows achieving the following layer characteristics:                metallic appearance        crack-free surface        high hardness along the edges, abrasion-resistance and scratch resistance        impact-resistant surface        high adherence between the layer and the substrate        layer build-up without influencing the surface topography        chemical resistance, in particular corrosion-resistance.        
A coating technique should furthermore be made available, which ensures the production of the desired layer structure and which is distinguished by:                an environment-friendly processing technique        economic production through integration of all processing steps in one and the same processing environment.        